diff --git a/src/js/i18n/i18n.ts b/src/js/i18n/i18n.ts
index e0c80f70..893c082c 100644
--- a/src/js/i18n/i18n.ts
+++ b/src/js/i18n/i18n.ts
@@ -1,5 +1,8 @@
 import i18next from 'i18next';
 import HttpBackend from 'i18next-http-backend';
+import { getStoredItem, setStoredItem } from '../utils/safe-storage.js';
+import enCommon from '../../../public/locales/en/common.json';
+import enTools from '../../../public/locales/en/tools.json';
 
 // Supported languages
 export const supportedLanguages = [
@@ -73,7 +76,7 @@ export const getLanguageFromUrl = (): SupportedLanguage => {
     return langMatch[1] as SupportedLanguage;
   }
 
-  const storedLang = localStorage.getItem('i18nextLng');
+  const storedLang = getStoredItem('i18nextLng');
   if (
     storedLang &&
     supportedLanguages.includes(storedLang as SupportedLanguage)
@@ -110,7 +113,7 @@ export const initI18n = async (): Promise<typeof i18next> => {
 
   const currentLang = getLanguageFromUrl();
 
-  localStorage.setItem('i18nextLng', currentLang);
+  setStoredItem('i18nextLng', currentLang);
 
   await i18next.use(HttpBackend).init({
     lng: currentLang,
@@ -119,6 +122,13 @@ export const initI18n = async (): Promise<typeof i18next> => {
     ns: ['common', 'tools'],
     defaultNS: 'common',
     preload: [currentLang],
+    partialBundledLanguages: true,
+    resources: {
+      en: {
+        common: enCommon,
+        tools: enTools,
+      },
+    },
     backend: {
       loadPath: `${import.meta.env.BASE_URL.replace(/\/?$/, '/')}locales/{{lng}}/{{ns}}.json`,
     },
@@ -139,7 +149,7 @@ export const t = (key: string, options?: Record<string, unknown>): string => {
 
 export const changeLanguage = (lang: SupportedLanguage): void => {
   if (!supportedLanguages.includes(lang)) return;
-  localStorage.setItem('i18nextLng', lang);
+  setStoredItem('i18nextLng', lang);
 
   const basePath = import.meta.env.BASE_URL.replace(/\/$/, '');
   let relativePath = window.location.pathname;
diff --git a/src/js/main.ts b/src/js/main.ts
index 755aae23..2e3411b1 100644
--- a/src/js/main.ts
+++ b/src/js/main.ts
@@ -22,6 +22,11 @@ import {
   isToolDisabled,
   isCurrentPageDisabled,
 } from './utils/disabled-tools.js';
+import {
+  getStoredItem,
+  setStoredItem,
+  removeStoredItem,
+} from './utils/safe-storage.js';
 declare const __BRAND_NAME__: string;
 
 const init = async () => {
@@ -290,17 +295,14 @@ const init = async () => {
 
     let collapsedCategories: string[] = [];
     try {
-      const stored = localStorage.getItem('collapsedCategories');
+      const stored = getStoredItem('collapsedCategories');
       if (stored) collapsedCategories = JSON.parse(stored);
     } catch {
-      localStorage.removeItem('collapsedCategories');
+      removeStoredItem('collapsedCategories');
     }
 
     function saveCollapsedCategories() {
-      localStorage.setItem(
-        'collapsedCategories',
-        JSON.stringify(collapsedCategories)
-      );
+      setStoredItem('collapsedCategories', JSON.stringify(collapsedCategories));
     }
 
     const filteredCategories = categories
@@ -615,7 +617,7 @@ const init = async () => {
   ) as HTMLInputElement;
   const toolInterface = document.getElementById('tool-interface');
 
-  const savedFullWidth = localStorage.getItem('fullWidthMode') !== 'false';
+  const savedFullWidth = getStoredItem('fullWidthMode') !== 'false';
   if (fullWidthToggle) {
     fullWidthToggle.checked = savedFullWidth;
     applyFullWidthMode(savedFullWidth);
@@ -652,7 +654,7 @@ const init = async () => {
   if (fullWidthToggle) {
     fullWidthToggle.addEventListener('change', (e) => {
       const enabled = (e.target as HTMLInputElement).checked;
-      localStorage.setItem('fullWidthMode', enabled.toString());
+      setStoredItem('fullWidthMode', enabled.toString());
       applyFullWidthMode(enabled);
     });
   }
@@ -661,7 +663,7 @@ const init = async () => {
     'compact-mode-toggle'
   ) as HTMLInputElement;
 
-  const savedCompactMode = localStorage.getItem('compactMode') === 'true';
+  const savedCompactMode = getStoredItem('compactMode') === 'true';
   if (compactModeToggle) {
     compactModeToggle.checked = savedCompactMode;
   }
@@ -681,7 +683,7 @@ const init = async () => {
   if (compactModeToggle) {
     compactModeToggle.addEventListener('change', (e) => {
       const enabled = (e.target as HTMLInputElement).checked;
-      localStorage.setItem('compactMode', enabled.toString());
+      setStoredItem('compactMode', enabled.toString());
       applyCompactMode(enabled);
     });
   }
diff --git a/src/js/utils/safe-storage.ts b/src/js/utils/safe-storage.ts
new file mode 100644
index 00000000..a8149d6d
--- /dev/null
+++ b/src/js/utils/safe-storage.ts
@@ -0,0 +1,25 @@
+export const getStoredItem = (key: string): string | null => {
+  try {
+    return localStorage.getItem(key);
+  } catch {
+    return null;
+  }
+};
+
+export const setStoredItem = (key: string, value: string): boolean => {
+  try {
+    localStorage.setItem(key, value);
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+export const removeStoredItem = (key: string): boolean => {
+  try {
+    localStorage.removeItem(key);
+    return true;
+  } catch {
+    return false;
+  }
+};
diff --git a/src/tests/i18n-resilience.test.ts b/src/tests/i18n-resilience.test.ts
new file mode 100644
index 00000000..0eb1a990
--- /dev/null
+++ b/src/tests/i18n-resilience.test.ts
@@ -0,0 +1,54 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+const blockStorage = () => {
+  Object.defineProperty(window, 'localStorage', {
+    configurable: true,
+    get() {
+      throw new DOMException('The operation is insecure.', 'SecurityError');
+    },
+  });
+};
+
+const failLocaleFetches = () => {
+  vi.stubGlobal(
+    'fetch',
+    vi.fn(() => Promise.reject(new TypeError('NetworkError')))
+  );
+};
+
+describe('i18n resilience on hardened browsers', () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.unstubAllGlobals();
+  });
+
+  it('getLanguageFromUrl does not throw when localStorage access is blocked', async () => {
+    blockStorage();
+    const { getLanguageFromUrl } = await import('../js/i18n/i18n');
+    expect(() => getLanguageFromUrl()).not.toThrow();
+    expect(getLanguageFromUrl()).toBe('en');
+  });
+
+  it('initI18n succeeds with blocked storage and failing locale fetches', async () => {
+    blockStorage();
+    failLocaleFetches();
+    const { initI18n, t } = await import('../js/i18n/i18n');
+    await expect(initI18n()).resolves.toBeDefined();
+    expect(t('simpleMode.title')).not.toBe('simpleMode.title');
+  });
+
+  it('t() serves bundled English instead of raw keys when fetches fail', async () => {
+    failLocaleFetches();
+    const { initI18n, t } = await import('../js/i18n/i18n');
+    await initI18n();
+    expect(t('simpleMode.title')).toBe('PDF Tools');
+    expect(t('tools:pdfToTiff.name')).toBe('PDF to TIFF');
+    expect(t('common.error')).not.toBe('common.error');
+  });
+
+  it('changeLanguage does not throw when storage is blocked', async () => {
+    blockStorage();
+    const { changeLanguage } = await import('../js/i18n/i18n');
+    expect(() => changeLanguage('de')).not.toThrow();
+  });
+});